Friends are double dosing: Marijuana and Prozac

Originally Published: September 17, 1999 - Last Updated / Reviewed On: December 30, 2008
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Dear Alice,

I have two friends who were recently diagnosed with depression. They were both prescribed Prozac by their respective doctors. Both of them are heavy marijuana users and both failed to mention that to their doctors. One has been on Prozac for two months and the other for six weeks. I have noticed that their behavior has become strange: mood swings, paranoia, oversleeping, fatigue. They continue taking their Prozac (20 mg a day) and continue smoking pot. I am afraid that there might be some negative interaction between the substances, one being an anti-depressant and the other a depressant. Can you provide some insight?

— Concerned Friend

Dear Concerned Friend,

You're smart to have questions about combining anti-depressants and other substances. Indeed, whenever taking a prescription drug, a thorough discussion with a health care provider is necessary to minimize negative effects and maximize positive ones.

Prozac is the brand name for fluoxetine, an anti-depressant in the class known as selective serotonin reuptake inhibitors (SSRIs). These drugs affect your brain's ability to absorb serotonin, a neurotransmitter that is involved in the regulation of emotions and mood. Prozac is perhaps the most well known of the many different medications prescribed to help people whose symptoms of depression are caused by an imbalance of chemicals in the brain. Marijuana, in its own drug class, is not a strict depressant. It has different effects based on the user's mood, surroundings, dose, and frequency of use. These can range from sedative to hallucinogenic to stimulant.

One of the most important factors when combining drugs — whether they be prescription or over-the-counter, controlled or illicit — is to be able to measure if and how much each drug is affecting mood and behavior, and what side effects each has. This is particularly important in a case such as this; presumably your friends are taking Prozac in the hopes that it will bring them relief from recurring, unpleasant feelings. Interestingly, marijuana and Prozac can actually produce many of the same emotional effects.

Some of the most common side effects of Prozac include nervousness, drowsiness, and anxiety; in some people, the anxiety is expressed as intense excitability. Some people experience insomnia while taking it. It's possible that these are the changes you've noticed in your friends. On the other hand, marijuana is also known to cause mood swings, sleepiness or sluggishness, and, sometimes, decreased motivation. In higher doses, hallucinogenic effects are possible, which may be expressed through anxiety or rapid changes in mood. Sometimes marijuana is laced with other drugs, like PCP, and then misperceptions, or even a sense of paranoia, are even more likely. Marijuana use can also cause some of the symptoms of depression, particularly in heavy users (which you say your friends are). There's a possibility that the emotional states your friends were experiencing (before being prescribed Prozac) were caused, or at least worsened, by their marijuana use. If they stopped or lightened up a bit on their use, they might find that they felt better, perhaps even without the anti-depressant.

There are also some other things to consider. Marijuana impairs the ability to concentrate and alters one's perceptions. Schoolwork, job responsibilities, and, particularly, driving a car or operating machinery may become more difficult. Prozac can also affect motor and decision-making skills, as well as perception. When a person first starts taking an anti-depressant, it's usually advised that activities like driving, climbing ladders, or using power tools are avoided until it's determined that it would be safe to do so. Combining Prozac and marijuana may increase the likelihood of an accident. It may also make it hard to decide if it would be safe to do these things if Prozac were being used alone. In addition, marijuana has been found to decrease the effect of Prozac. Using the two drugs together could make it hard to determine whether Prozac is actually useful for your friends, and if so, appropriate dosing.

It's really important that your friends talk with their health care providers about these issues. As a friend, you can provide them with this information, expressing your concern for their well-being. They're lucky to have someone as observant and caring as you are looking out for them.

Alice