HEALTHNET

Why do some medicines make me feel sleepy?

Antihistamines are widely prescribed; sleepiness is one of the most common side effects encountered.

(Posted on 9 November 2006)

Q1. Why do some medicines make me feel sleepy?

A1. Nerves and muscles connect and communicate through chemicals. Most drugs work by mimicking, blocking, increasing, or decreasing these chemicals.

Many drugs acting on the nervous system would cause sleepiness. Examples are drugs used to treat epilepsy, and medicine prescribed for severe pain. Most sedatives (drugs used to sedate a patient) and anxiolytics (drugs used to relieve anxiety) would cause sleepiness.

Blood vessels in our brain can prevent some drugs, but not all, from entering the central nervous system. Since there is a lot of fatty material in the nervous system, drugs that have a small molecular size and are soluble in fat would get into the brain more readily.

Antihistamines also cause sleepiness. Antihistamines are drugs that can block the action of histamine, a chemical that is used as a signal in many types of cells in our body. Since antihistamines are widely prescribed for cough and colds, allergic symptoms and skin diseases, sleepiness is one of the most common side effects encountered. Fortunately, many newer preparations of antihistamines do not enter the brain, and hence would not make you sleepy. Under certain circumstances, sleepiness can be a desirable effect, such as treating an allergic skin condition that is disturbing a patient's sleep.

Q2. What should I do if I can't sleep after taking a drug?

A2. Caffeine is a common ingredient in proprietary cold tablets, which adds into your daily coffee quota. Many other drugs also have stimulant properties on our nervous system, and can prevent us from falling asleep.

Decongestants are a class of drugs that can shrink blood vessels supplying to membranes in our noses, and are often used in cough and colds. These drugs can enter the brain, make you nervous, easily get agitated and cannot fall sleep. You may feel that your heart is beating crazy. Little wonder, this class of drugs is chemically related to adrenaline, the stress hormone. They stimulate the heart and increase the blood pressure. Drugs used to suppress the appetite and drugs used in hyperactive children may also cause sleep problems as well as similar side effects.

If you have trouble falling asleep and you suspect that the drug you have been taking is the culprit, check your doctor's instructions whether it is absolutely necessary to continue with the drug. Symptoms of cough and cold usually improve spontaneously without specific treatment. Remember, a good night's rest is just as essential for healing. If your condition demands that you continue with the drug, try taking the drug as earlier as practicable. You may also split your daily dose into two to space out the effect on your body. You should avoid taking alcohol and caffeinated drinks while on medicine.

Q3. Some drugs make me feel dizzy. Should I ask my doctor to prescribe a different medicine?

A3. You should always tell your doctor if you suspect prescribed drugs have made you feel uncomfortable. Most doctors would welcome your feedback. But if your doctor is not immediately available, you should stop taking the drug unless the doctor has made clear instructions that you must finish a course of treatment.

Different people may have different experiences with a drug. Drugs that cause sleepiness can also make you dizzy. People may experience dizziness when the blood pressure is too low or too high. Elderly people, especially those who are under treatment for hypertension should be careful. Drugs may interact with each other and affect their effectiveness.

Very often a patient's perceived side effects are just coincidental. New symptoms that appear after taking a drug may signify a change in your clinical condition. For example, dizziness may be a symptom of bleeding into the gastrointestinal tract, which needs to be taken care of in a hospital.

Drugs such as antihistamines have evolved into newer generations that do not enter the brain. They are less likely to cause sleepiness and dizziness. You should ask your doctor if alternatives are available.

Source: Quality HealthCare