Caffeine is one of the most consumed psychostimulants in the world (compounds that stimulate brain activity). It can be found in coffee beans, teas, cocoa and energy drinks.
Despite its widespread use, caffeine can interact with certain medications, affecting how they work, how long they last in the body, and how your body absorbs them.
Interactions between caffeine and other drugs can lead to increased side effects and toxicity, make the drug less effective, or cause unexpected health complications.
Blood thinners such as aspirin, Plavix (clopidogrel), and warfarin (brand names like Coumadin and Jantoven) prevent blood clotting. A healthcare professional may recommend blood thinners if you have heart or blood conditions such as stroke or to reduce the risk of blood clots after surgery.
One of the most common side effects of blood thinners is bleeding. Like blood thinners, caffeine can slow blood clotting. Taking caffeine with these medications can increase the risk of bruising and bleeding.
Some studies show that caffeine can moderately increase the absorption rate of blood thinners like aspirin and how much is available to the body, making the side effect of bleeding more pronounced.
Sudafed (pseudoephedrine) is a medication that treats stuffy or stuffy noses caused by colds or allergies.
Just like caffeine, pseudoephedrine is a stimulant. When used together, the drugs can produce a double effect, making you feel more jittery, restless, and irritable.
Some studies also show that combining pseudoephedrine with caffeine can raise blood sugar and raise body temperature, which can be dangerous for people living with diabetes.
It is best to avoid caffeine while using pseudoephedrine or to space them out by about 5-6 hours.
Birth control pills or oral contraceptives such as Micronor (norethindrone) or Sprintec (norgestimate/ethinyl estradiol) are medications taken by mouth to prevent pregnancy.
Research has shown that using oral contraceptives can double the half-life of caffeine, making it last twice as long. Because the effects of caffeine last longer than normal, you may experience increased symptoms such as insomnia, restlessness, or stomach discomfort.
Lexapro (escitalopram), Elavil (amitriptyline), and Tofranil (imipramine) are common medications prescribed to treat symptoms of depression.
Research shows that caffeine forms a complex with escitalopram when used together. This complex reduces the amount of escitalopram available for action in the body, which may reduce its effectiveness.
Caffeine can increase the amount of imipramine concentration in the brain, which can lead to increased effects of antidepressants.
Other studies have found that caffeine can increase the concentration of amitriptyline in the blood by slowing its elimination from the body. This can increase the risk of side effects such as constipation, dizziness, dry mouth and drowsiness.
Antibiotics are drugs that kill or inhibit the growth of bacteria. Your healthcare provider may prescribe them to treat conditions such as strep throat, urinary tract infections (UTIs), and pneumonia.
Research shows that caffeine inhibits the action of some antibiotics, such as Avelok (moxifloxacin), Norokin (norfloxacin), Cipro (ciprofloxacin), and Chloromycetin (chloramphenicol). Caffeine can make these drugs less effective at fighting infections.
Teochron (theophylline) is a medicine used to treat severe asthma and chronic obstructive pulmonary disease (COPD).
Caffeine and theophylline are stimulants in the same class of drugs: methylxanthines. When used together, caffeine can increase the side effects of theophylline, such as headache, tremors, vomiting, insomnia, and increased blood pressure and heart rate.
It is recommended that people taking theophylline be careful about consuming food or drinks with a high caffeine content, as this combination may increase the risk of side effects.
Zanaflex (tizanidine) is a medicine used to relieve muscle spasms. It is usually prescribed to treat conditions such as multiple sclerosis (MS), spinal cord injury or stroke.
Tizanidine and caffeine are metabolized by the same enzyme, CIP1A2. Taking them together can increase the risk of tizanidine side effects, such as low blood pressure, which can lead to falls and fractures.
Synthroid (levothyroxine) is a drug used to treat hypothyroidism, a condition in which the thyroid gland does not produce enough thyroid hormone.
Caffeine can slow the absorption of levothyroxine, potentially reducing the effectiveness of levothyroxine in the treatment of hypothyroidism. This interaction is especially pronounced when both drugs are taken within an hour of each other.
It is recommended that you wait at least four hours between consuming caffeine and taking levothyroxine to minimize this interaction.
Caffeine may not interact directly with medications used to lower blood pressure, but it can moderate their effects, especially when consumed in large amounts.
Two types of blood pressure medications affected by this interaction are beta-blockers (propranolol, known as Inderal) and diuretics (furosemide, known as Lasik). Research has shown that caffeine can counteract these drugs, reducing their effectiveness in lowering blood pressure.
Risedronate (brand names such as Actonel and Atelvia) and Fosamax (alendronate) are drugs used to treat and prevent osteoporosis.
Coffee and other caffeinated beverages can reduce the absorption of oral osteoporosis drugs such as risedronate and alendronate, making them less effective.
Studies also show that high concentrations of caffeine can interfere with calcium absorption, which supports bone health. People prone to osteoporosis should avoid caffeine completely.
Galantamine, rivastigmine, and donepezil are approved for the treatment of mild to moderate Alzheimer’s disease.
To effectively treat memory loss, Alzheimer’s treatments must cross the blood-brain barrier (BBB) to reach the brain, where they can exert their effects. Caffeine can prevent the BBB from opening, making it harder for these drugs to reach the brain.
Methotrexate is a drug used to treat psoriasis, especially forms that cannot be controlled by other treatments. It may also be prescribed to treat certain types of cancer, such as breast and lung cancer and leukemia.
Caffeine has been found to reduce the beneficial effects of methotrexate, particularly its anti-inflammatory effects. This may be due to the antagonistic effect of caffeine on adenosine receptors, which methotrexate also targets.
However, other studies have found that caffeine can enhance the effects of methotrexate, so it is best to consult a doctor before using this combination.
Caffeine is generally safe and well tolerated, especially when consumed at less than 400 milligrams per day.
Caffeine can interact with drugs such as warfarin, levothyroxine, and theophylline, potentially increasing the drug’s side effects or performance.
If you regularly consume caffeine and start taking a new medication or have an underlying medical condition, it’s best to consult your doctor about possible interactions.
You should also see your doctor if you experience any side effects, such as increased restlessness, agitation, insomnia, hallucinations, or any other unusual symptoms.
Here are some ways you can reduce or limit caffeine if you are taking medications that can affect it:
- To prevent withdrawal symptoms, gradually reduce your daily caffeine intake (eg if you consume four cups of caffeinated drinks, reduce it to two)
- Swap caffeinated tea or coffee for a decaffeinated version
- Avoid caffeine consumption at night and within 5-6 hours of taking the medicine
- For caffeinated teas, brew for less time to reduce caffeine
- Seek professional advice if cutting back on caffeine is overwhelming
Caffeine can be part of a healthy diet for most people. However, it may pose a health risk depending on your current medications, certain medical conditions, and age.
If you’re a caffeine lover, it’s best to talk to your doctor or pharmacist about how caffeine might interact with your medications before you start taking it.
Contact your doctor if you experience any of the following symptoms while using caffeine and any medication: increased restlessness, sleep disturbance, fast heart rate, anxiety, nervousness, or palpitations.