Guide to common drug interactions

Drug	Interacting drug	Effect

Over-the-counter drugs and substances
Antacids
Alumina and magnesia				Effects of dicumarol may be faster and/or
Dihydroxyaluminum sodium				 	increased
	carbonate				
Magnesia
			Digoxin	Effects of digoxin may be reduced

			Tetracyclines	Effects of tetracyclines may be reduced
				Doxycycline	Should be taken 1-3 hours apart
				Tetracycline

Painkillers
Acetaminophen	Alcoholic beverages	May cause liver damage
Buffered acetaminophen
			Blood-thinning drugs	High doses of acetaminophen may increase
				Warfarin sodium		blood-thinning effects of these drugs

			Tetracycline	Buffered form may cancel the effects of
							tetracycline
						Should be taken 1 hour apart

Ibuprofen	Alcoholic beverages	May cause internal bleeding or ulcers

			Blood-thinning drugs	May cause internal bleeding or ulcers
				Heparin
				Warfarin sodium

			Salicylates	May cause stomach upset without relieving
				Aspirin		symptoms
				Aspirin and caffeine
				Buffered aspirin

Salicylates	Alcoholic beverages	May cause stomach ulcers or internal
		Aspirin					bleeding
		Aspirin and caffeine
		Buffered aspirin	Antidiabetics	May cause blood sugar level to drop too
				Chlorpropamide		low
				Tolazamide

			Blood-thinning drugs	Increases risk of internal bleeding
				Heparin
				Warfarin sodium

			Ibuprofen	May cause stomach upset without relieving
							symptoms

			Tetracycline	Effects of tetracycline are reduced

Other substances
Alcoholic beverages	Acetaminophen	May cause liver damage
			Buffered acetaminophen

			Antidiabetics	Stomach upset, vomiting, cramps,
				Chlorpropamide		headaches, low blood sugar
				Tolazamide

			Antiseizure drugs	May cause extreme drowsiness
				Carbamazepine
				Chlordiazepoxide
				Diazepam
				Phenytoin

			Barbiturates	May cause drowsiness, increase effects of
				Pentobarbital		either drug, cause breathing to fail, or
				Phenobarbital		cause blood pressure to drop too low
				Secobarbital
				Secobarbital and amobarbital

			Ibuprofen	May cause internal bleeding or ulcers

			Narcotic analgesics	May depress nervous system and breathing
				Acetaminophen and codeine		or cause blood pressure to drop too low
				Meperidine
				Propoxyphene

			Reserpine	May increase effects of alcohol and
							reserpine

			Salicylates	May cause stomach ulcers or internal
				Aspirin		bleeding
				Aspirin and caffeine
				Buffered aspirin

			Tricyclic antidepressants	May cause extreme drowsiness
				Amitriptyline
				Amoxapine
				Doxepin

Sodium chloride (salt)	Lithium	Low-salt diet causes lithium to build up in
							body and is not advised

Tobacco (smoking)	Birth control pills	May increase chances of blood clot or
				Norethindrone with ethinyl estradiol		heart attack

Tyramine-containing foods:	MAO inhibitors	May cause severe and sometimes fatal high
	Avocados, bananas, beer,		 Isocarboxazid		blood pressure
		caffeine,cheese, chicken		Phenelzine	Headache, vomiting, fever, and high blood
		liver, chocolate, fava beans,		Tranylcypromine		pressure are warning signals
		fermented sausages (salami, 
		pepperoni, bologna, etc.), 
		canned figs, pickled herring,
		pineapple, raisins, red wine, 
		sauerkraut, soy sauce, yeast 
		extract, yogurt

Prescription drugs
Antibiotics
Erythromycins	Penicillins	Could interfere with the effects of
	Erythromycin		Amoxicillin		penicillins
	Erythromycin lactobionate		Ampicillin
Penicillins
	Amoxicillin	Birth control pills	May interfere with and result in unplanned
	Ampicillin		Norethindrone with ethinyl estradiol		pregnancy or menstrual problems

			Blood-thinning drugs	May increase blood thinning effects of
				Warfarin sodium		these drugs

			Erythromycins	May interfere with effects of penicillins
				Erythromycin
				Erythromycin lactobionate

			Tetracyclines	May interfere with effects of penicillins
				Doxycycline
				Tetracycline

Tetracyclines	Acetaminophen
	Doxycycline	Buffered acetaminophen
	Tetracycline
			Antacids	May decrease effects of tetracyclines and
				Alumina and magnesia		should be taken 1 to 3 hours apart
				Dihydroxyaluminum sodium carbonate
				Magnesia

			Barbiturates	May decrease effects of doxycycline
				Pentobarbital	Other tetracyclines can be used
				Phenobarbital
				Secobarbital
				Secobarbital and amobarbital

			Penicillins	May interfere with effects of penicillins
				Amoxicillin
				Ampicillin

			Salicylates	Effects of tetracyclines are reduced
				Aspirin
				Aspirin and caffeine
				Buffered aspirin

Antidepressants
Lithium	Sodium chloride (salt)	Low-salt diet causes lithium to build up in
							body and is not advised

			Thiazide diuretics	May cause lithium to have toxic effect
				Furosemide
				Methyclothiazide

Tricyclic antidepressants	Alcoholic beverages	May cause extreme drowsiness
	Amitriptyline
	Amoxapine	Antiseizure drugs	Effects of antiseizure drug may be
	Doxepin		Carbamazepine		decreased
				Chlordiazepoxide	Dosage should be adjusted
				Diazepam
				Phenytoin

			Blood-thinning drugs	May cause internal bleeding
				Warfarin sodium

			MAO inhibitors	Severe seizure and death could result
				Isocarboxazid
				Phenelzine	Should be taken 14 days apart
				Tranylcypromine

			Narcotic analgesics	May depress nervous system and breathing
				Acetaminophen and codeine		and cause blood pressure to drop too low
				Meperidine
				Propoxyphene

Antidiabetics
Chlorpropamide	Alcoholic beverages	May cause stomach upset, vomiting,
Tolazamide					cramps, headaches, low blood sugar

			Beta-adrenergic blockers	May increase risk of either high or low
				Metoprolol		blood sugar levels
				Propranolol	May mask symptoms

			Blood-thinning drugs	Blood-thinning effect will be increased at
				Warfarin sodium		first, later it will be decreased
						May also cause low blood sugar and
							become toxic

			MAO inhibitors	Can cause extreme low blood sugar level
				Isocarboxazid
				Phenelzine
				Tranylcypromine

			Salicylates	May cause blood sugar level to drop too
				Aspirin		low
				Aspirin and caffeine
				Buffered aspirin

Isophane insulin suspension	Beta-adrenergic blockers	These may mask symptoms of low blood
				Metoprolol		sugar
				Propranolol

			Birth control pills	May increase risk of high blood sugar
				Norethindrone with ethinyl estradiol		levels
						Dosages should be adjusted

			MAO inhibitors	May cause extreme low blood sugar level
				Isocarboxazid
				Phenelzine
				Tranylcypromine

Antiseizure drugs
Carbamazepine	Alcoholic beverages	May cause extreme drowsiness
Chlordiazepoxide
Diazepam	Beta-adrenergic blockers	Could decrease the effect of beta-blockers
Phenytoin		Metoprolol
				Propranolol

			Birth control pills	Phenytoin and carbamazepine may interfere
				Norethindrone with ethinyl estradiol		and increase risk of unplanned pregnancy
					May increase effect of diazepam

			Tricyclic antidepressants	Effects of antiseizure drug may be
				Amitriptyline		decreased
				Amoxapine	Dosage should be adjusted
				Doxepin

Barbiturates
Pentobarbital	Alcoholic beverages	May cause drowsiness, increase effects of
Phenobarbital					either drug, cause breathing to fail, or
Secobarbital					cause blood pressure to drop too low
Secobarbital and
	 amobarbital
			Birth control pills	Barbiturates may interfere with and result
				Norethindrone with ethinyl estradiol		in unplanned pregnancy

			Blood-thinning drugs	May decrease blood-thinning effects of
				Warfarin sodium		these drugs

			Doxycycline	May decrease effects of doxycycline
					Other tetracyclines can be used
Birth control pills
Norethindrone with ethinyl	Antiseizure drugs	Will increase the sedative effects of these
	estradiol		Carbamazepine		drugs
				Chlordiazepoxide	May decrease the effects of other
				Diazepam		antiseizure drugs
				Phenytoin

			Barbiturates	Barbiturates may interfere with birth
				Pentobarbital		control pills and result in unplanned
				Phenobarbital		pregnancy
				Secobarbital
				Secobarbital and amobarbital

			Isophane insulin suspension	May increase risk of high blood sugar
							levels; dosages should be adjusted

			Penicillins	May interfere with birth control pills and
				Amoxicillin		result in unplanned pregnancy
				Ampicillin

			Tobacco (smoking)	May increase chances of blood clot or
							heart attack

Blood pressure drugs
Thiazide diuretics	Beta-adrenergic blockers	Can cause extremely low blood pressure
	Furosemide		Metoprolol
	Methyclothiazide		Propranolol

			Digitalis glycosides	Can cause irregular heartbeat, which can
				Digoxin		be fatal
						Can cause extremely low blood pressure

			Lithium	May cause lithium to have toxic effect
			Reserpine	Can cause extremely low blood pressure
Rauwolfia alkaloids	Alcoholic beverages	May increase effects of alcohol
	Reserpine				May increase effects of rauwolfia alkaloids

			Beta-adrenergic blockers	May cause extremely slow heartbeat and
				Metoprolol		low blood pressure
				Propranolol

			Digitalis glycosides	May cause irregular heartbeat
				Digoxin

			MAO inhibitors	May cause slight to sudden and severe high
				Isocarboxazid		blood pressure
				Phenelzine	May cause extreme high fever
				Tranylcypromine	Either effect could be life-threatening

			Thiazide diuretics	Can cause extreme low blood pressure
				Furosemide
				Methyclothiazide

Blood-thinning drugs
Warfarin sodium	Acetaminophen	High doses of acetaminophen may increase
			Buffered acetaminophen		blood-thinning effects of these drugs

			Antacids	Effects of dicumarol may be faster and
				Alumina and magnesia		may also be increased
				Dihydroxyaluminum sodium carbonate
				Magnesia

			Antidiabetics	Blood-thinning effect will be increased at
				Chlorpropamide		first, later it will be decreased
				Tolazamide	May also cause low blood sugar and
							become toxic

			Barbiturates	Decreases blood-thinning effect
				Pentobarbital
				Phenobarbital
				Secobarbital
				Secobarbital and amobarbital

			Heparin	May cause increased risk of internal
							bleeding		

			Ibuprofen	May cause internal bleeding or ulcers

			Penicillins	May increase blood-thinning effects of
				Amoxicillin		these drugs
				Ampicillin

			Salicylates	Blood-thinning effects will be increased
				Aspirin	May cause ulcers or internal bleeding
				Aspirin and caffeine
				Buffered aspirin
	
			Tricyclic antidepressants	May cause internal bleeding
				Amitriptyline
				Amoxapine
				Doxepin

Heparin	Blood-thinning drugs	May cause increased risk of internal
				Warfarin sodium		bleeding

			Salicylates	Blood-thinning effects will be increased
				Aspirin	May cause ulcers or internal bleeding
				Aspirin and caffeine
				Buffered aspirin

Heart drugs
Beta-adrenergic blockers	Antidiabetics	May increase risk of either high or low
	Metoprolol		Chlorpropamide		blood sugar levels
	Propranolol		Tolazamide	May mask symptoms
				
			Antiseizure drugs	Could decrease the effect of beta blockers
				Carbamazepine
				Chlordiazepoxide
				Diazepam
				Phenytoin

			Digitalis glycosides	May cause extremely slow heartbeat with a
				Digoxin		chance of heart block

			Isophane insulin suspension	Beta blockers may mask symptoms of low
							blood sugar
						May also cause low blood sugar

			Reserpine	May cause extremely slow heartbeat and
						low blood pressure

			Thiazide diuretics	Can cause extremely low blood pressure
				Furosemide
				Methyclothiazide

Digitalis glycosides	Antacids	Effects of digoxin may be reduced
	Digoxin		Alumina and magnesia
				Dihydroxyaluminum sodium carbonate
				Magnesia

			Beta-adrenergic blockers	May cause extremely slow heartbeat with a
				Metoprolol		chance of heart block
				Propranolol
			Reserpine	May cause irregular heartbeat

			Thiazide diuretics	May cause extreme low blood pressure;
				Furosemide		may cause digitalis to become toxic
				Methyclothiazide

Monoamine oxidase inhibitors (MAO inhibitors)
Isocarboxazid	Antidiabetics	Can cause extreme low blood sugar level
Phenelzine		Chlorpropamide
Tranylcypromine		Isophane insulin suspension
				Tolazamide

			Narcotic analgesics	May cause severe and sometimes fatal
				Acetaminophen and codeine		reactions
				Meperidine
				Propoxyphene

			Reserpine	May cause slight to sudden and severe high
							blood pressure
						May cause extreme high fever
						Either effect could be life-threatening

			Tricyclic antidepressants	Severe seizure and death could result
				Amitriptyline	Should be taken 14 days apart
				Amoxapine
				Doxepin

			Tyramine-containing foods	May cause severe and sometimes fatal high
				Avocados, bananas, beer, caffeine,		blood pressure.
					cheese, chicken liver, chocolate, fava	Headache, vomiting, fever, and high blood
					beans, fermented sausages (salami,		pressure are warning signals
					pepperoni, bologna, etc.) canned figs,
					pickled herring, pineapple, raisins, red
					wine, sauerkraut, soy sauce, yeast
					extract, yogurt

Painkillers
Narcotic analgesics	Alcoholic beverages	May depress nervous system and breathing
	Acetaminophen and codeine				May cause blood pressure to drop too low
	Meperidine
	Propoxyphene	MAO inhibitors	May cause many severe and sometimes
				Isocarboxazid		fatal reactions
				Phenelzine
				Tranylcypromine

			Tricyclic antidepressants	May depress nervous system and breathing
				Amitriptyline	May cause blood pressure to drop too low
				Amoxapine
				Doxepin

This table includes only common over-the-counter and prescription drugs.  Some of these drugs may also interact with less 
common drugs and substances not described.  When using any drug, always consult your doctor or pharmacist about 
possible interactions with other drugs, substances, or foods.