Delta-9-tetrahydrocannabinol (THC) is a cannabinoid found in cannabis (Cannabis sativa). The psychoactive effects of cannabis are mainly due to THC.
There are over 80 cannabinoids in Cannabis sativa, but THC and cannabidiol (CBD) are the most well-studied. THC works by binding to specific sites in the brain and on the nerves. It's found in the highest levels in the leaves and flowers of the plant.
THC is commonly used as a recreational drug. People also use THC for multiple sclerosis (MS), nerve pain, nausea and vomiting from chemotherapy, alcohol use disorder, and many other conditions, but there is no good scientific evidence to support these uses. There is also no good evidence to support using THC for COVID-19.
Don't confuse THC with other cannabinoids found in cannabis, including cannabichromene (CBC), cannabidiol (CBD), cannabidivarin (CBDV), cannabigerol (CBG), cannabinol (CBN), delta-8-tetrahydrocannabinol (Delta-8-THC), or tetrahydrocannabivarin (THCV). Also don't confuse it with synthetic cannabinoids such as K2/Spice, or with plants containing THC, such as cannabis or hemp. These are not the same. THC is illegal on the federal level in the US. Due to its THC content, cannabis is classified as a Schedule I controlled substance. But some states have legalized or decriminalized recreational use.
Is It Effective?
There is interest in using THC for a number of purposes, but there isn't enough reliable information to say whether it might be helpful.
Is it Safe?
When taken by mouth: THC is possibly unsafe when used in large amounts or long-term. Edible cannabis containing 50 mg or more of THC has been linked with serious side effects. Regularly taking large amounts of THC might cause cannabinoid hyperemesis syndrome (CHS). CHS leads to severe nausea and vomiting that doesn't respond to typical anti-nausea drugs. Also, using THC for at least 1-2 weeks can cause dependence.
When inhaled: THC is possibly unsafe when used in large amounts or long-term. Smoking or vaping THC can cause breathing problems. Vaping products containing THC have been linked to serious lung injury. Regularly smoking cannabis containing THC may cause CHS and/or dependence.
Special Precautions & Warnings:
Pregnancy: Using THC is unsafe during pregnancy. The chemicals in cannabis, including THC, pass through the placenta and can slow the growth of the fetus and increase the risk for premature birth, stillbirth, childhood leukemia, abnormalities, or the need for intensive care after birth. It can also lead to lower intelligence and emotional problems in the child when they grow up. It also increases the risk for anemia and high blood pressure while pregnant.
Breast-feeding: Using THC is likely unsafe while breast-feeding. THC passes into breastmilk and stays in breastmilk for longer than 6 weeks, even after THC use has been stopped. This might slow down the development of the baby. Avoid all THC use if planning to breastfeed.
Bipolar disorder: Using THC might make manic symptoms worse in people with bipolar disorder.
Heart disease: THC might cause fast heartbeat and high blood pressure. It might also increase the risk of having a heart attack.
Epilepsy: High doses of THC might cause seizures in people with epilepsy. There have been several reports where high doses of cannabis that contains THC have caused seizures.
Schizophrenia: Using THC might make symptoms of schizophrenia worse.
Surgery: THC affects the central nervous system. It might slow the central nervous system too much when combined with anesthesia and other medications during and after surgery. Stop using THC at least 2 weeks before a scheduled surgery.
Alcohol
Interaction Rating=Moderate Be cautious with this combination.
Using THC with alcohol might increase the effects of alcohol on the central nervous system. This might increase the risk for some side effects, such as drowsiness and mood changes.
Anesthesia
Interaction Rating=Moderate Be cautious with this combination.
Using THC might increase how much anesthesia your doctor needs to give to you for surgery. Tell your doctor if you regularly use THC or cannabis. If possible, stop using THC at least 2 weeks before surgery.
Medications changed by the liver (Cytochrome P450 2C9 (CYP2C9) substrates)
Interaction Rating=Moderate Be cautious with this combination.
Some medications are changed and broken down by the liver. THC might change how quickly the liver breaks down these medications. This could change the effects and side effects of these medications.
Medications changed by the liver (Cytochrome P450 2E1 (CYP2E1) substrates)
Interaction Rating=Moderate Be cautious with this combination.
Some medications are changed and broken down by the liver. THC might change how quickly the liver breaks down these medications. This could change the effects and side effects of these medications.
Medications changed by the liver (Cytochrome P450 3A4 (CYP3A4) substrates)
Interaction Rating=Moderate Be cautious with this combination.
Some medications are changed and broken down by the liver. THC might change how quickly the liver breaks down these medications. This could change the effects and side effects of these medications.
Medications for dissolving blood clots (Thrombolytic drugs)
Interaction Rating=Moderate Be cautious with this combination.
THC might slow blood clotting. Taking THC with medications used for dissolving blood clots might increase the chance of bleeding and bruising.
Medications moved by pumps in cells (P-glycoprotein Substrates)
Interaction Rating=Moderate Be cautious with this combination.
Some medications are moved in and out of cells by pumps. THC might change how these pumps work and change how much medication stays in the body. In some cases, this might change the effects and side effects of a medication.
Medications that decrease the breakdown of other medications by the liver (Cytochrome P450 2C9 (CYP2C9) inhibitors)
Interaction Rating=Moderate Be cautious with this combination.
THC is changed and broken down by the liver. Some drugs decrease how quickly the liver changes and breaks down THC. This could change the effects and side effects of THC.
Medications that decrease the breakdown of other medications in the liver (Cytochrome P450 3A4 (CYP3A4) inhibitors)
Interaction Rating=Moderate Be cautious with this combination.
THC is changed and broken down by the liver. Some drugs decrease how quickly the liver changes and breaks down THC. This could change the effects and side effects of THC.
Medications that increase breakdown of other medications by the liver (Cytochrome P450 3A4 (CYP3A4) inducers)
Interaction Rating=Moderate Be cautious with this combination.
THC is changed and broken down by the liver. Some drugs increase how quickly the liver changes and breaks down THC. This could change the effects and side effects of THC.
Medications that increase the breakdown of other medications by the liver (Cytochrome P450 2C9 (CYP2C9) inducers)
Interaction Rating=Moderate Be cautious with this combination.
THC is changed and broken down by the liver. Some drugs increase how quickly the liver changes and breaks down THC. This could change the effects and side effects of THC.
Medications that slow blood clotting (Anticoagulant / Antiplatelet drugs)
Interaction Rating=Moderate Be cautious with this combination.
THC might slow blood clotting. Taking THC along with medications that also slow blood clotting might increase the risk of bruising and bleeding.
Sedative medications (Barbiturates)
Interaction Rating=Moderate Be cautious with this combination.
THC might cause sleepiness and slowed breathing. Some medications, called sedatives, can also cause sleepiness and slowed breathing. Taking THC with sedative medications might cause breathing problems and/or too much sleepiness.
Sedative medications (CNS depressants)
Interaction Rating=Moderate Be cautious with this combination.
THC might cause sleepiness and slowed breathing. Some medications, called sedatives, can also cause sleepiness and slowed breathing. Taking THC with sedative medications might cause breathing problems and/or too much sleepiness.
Theophylline
Interaction Rating=Moderate Be cautious with this combination.
Taking THC might decrease the effects of theophylline. But there isn't enough information to know if this is a big concern.
Warfarin (Coumadin)
Interaction Rating=Moderate Be cautious with this combination.
Using THC might increase the effects of warfarin. Smoking THC while taking warfarin might increase the chance of bruising and bleeding.
Herbs and supplements that cause sleepiness: THC might cause sleepiness and slowed breathing. Taking it along with other supplements with similar effects might cause too much sleepiness and/or slowed breathing in some people. Examples of supplements with this effect include hops, kava, L-tryptophan, melatonin, and valerian.
Herbs and supplements that might slow blood clotting: THC might slow blood clotting and increase the risk of bleeding. Taking it with other supplements with similar effects might increase the risk of bleeding in some people. Examples of supplements with this effect include garlic, ginger, ginkgo, nattokinase, and Panax ginseng.
There are no known interactions with foods.
THC is commonly used in capsules, edible products, sprays, vape products, and cigarettes. The effects and side effects of THC products can vary significantly depending on how much THC they contain. Concentrations range from 1% to 80% THC. Speak with a healthcare provider to find out what type of product and dose might be best for a specific condition.
THC is illegal under federal law in the US. Due to its THC content, cannabis is classified as a Schedule I controlled substance. Some states have legalized or decriminalized use.
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