CBD vs. THC: What's the Difference?

Medically Reviewed by Jabeen Begum, MD on October 31, 2023
Written by Mary Jo DiLonardo, Jennifer Walker-Journey
6 min read

You’ve probably heard a lot about marijuana as more and more states legalize it. It comes from the cannabis plant, which makes a thick substance full of compounds called cannabinoids. The cannabis plant produces more than 100 cannabinoids, including the two main ones, CBD and THC, which cause drug-like reactions in your body.

What is THC?

THC is delta-9-tetrahydrocannabinol, the main psychoactive ingredient in the cannabis plant. It’s what makes you feel “high” when you smoke marijuana or eat an edible.

Marijuana and other THC products are considered Schedule 1 controlled substances by the U.S. Drug Enforcement Agency (DEA). This means that the DEA considers them to have a high likelihood of being abused and no current medical use, despite marijuana being legal in some cities and states, including for medical purposes.

THC comes in three common forms, herbs or flowers, hash/hashish, and hash oil. The herbal variety is the most popular. It’s made from dried cannabis leaves and flowers, or buds, which you smoke or add to foods or drinks. 

Hash is a solid or paste-like substance that's made by compressing or purifying the resin from the buds. Hash oil, the most potent form, is made when the resin in hash is extracted into its purest form.

What is CBD?

CBD is short for cannabidiol. It’s also made from the cannabis plant. CBD is related to THC, but it’s not psychoactive, so it doesn’t make you “high” like THC does. CBD is easier to find in the U.S. than THC, but each state has different laws and restrictions on selling CBD.

CBD comes in many forms, including oils, extracts, patches, vapes, and topical lotions, and it's said to have various health benefits. It’s also the active ingredient in Epidiolex, the first medication made from a marijuana ingredient approved by the FDA to treat epilepsy.

CBD and THC both come from the same species of plant, Cannabis sativa. But there are major differences between the two.

CBD usually comes from the hemp plant, which is also a type of cannabis plant. Hemp contains very little THC, usually less than 0.3%. Cannabis plants with THC concentrations greater than 0.3% are considered marijuana.

THC and CBD come from the resin on the leaves and the buds of the female cannabis plants. CBD also comes from the flowering heads of the hemp plant.

Synthetic cannabinoids, also known as synthetic marijuana, Spice, or K2, are manufactured chemicals that mimic the high of THC. The psychoactive ingredients have different effects than THC and can cause serious reactions.

CBD and THC have the same molecular formula—21 carbon atoms, 30 hydrogen atoms, and two oxygen atoms. But the way the atoms are arranged is different, which is why they have distinct chemical properties and unique effects on your body.

Both affect the way your brain cells communicate with each other.

THC and CBD make you feel different when you use them. Here's how.

CBD effects

Scientists have identified several “molecular targets” in your body that can be affected by CBD.

But we're still not sure exactly how CBD works. Researchers think it slows down signals to your brain, lowers inflammation in your brain, and changes the level of calcium in your brain cells, which plays a role in communication between cells.

One serious issue with CBD products is what else they might contain. Most aren't regulated by the FDA, so nobody can guarantee their purity. One study on CBD products found that more than 25% contained less CBD than was listed on the label, and some also contained THC.

This could cause you to have a false positive result on a drug test. The FDA has issued several warnings to companies that market these products and says you should beware before you use them.

THC effects

THC in marijuana stimulates the parts of your brain that respond to pleasure. It also releases your body’s “feel good” hormone dopamine, giving you that relaxed, euphoric feeling.

The amount of THC in marijuana varies. The higher the level, the higher its potency, and the more effects it has on your body and brain. Today's marijuana plants are stronger than ever. The average strength of THC in marijuana is 15%, up from about 4% in the mid-1990s.

These higher levels could have some mental health effects on users, including:

  • Hallucinations
  • Delusions
  • Psychosis

People take CBD and THC in hopes of relieving a wide variety of physical and mental health symptoms.

While more studies are needed to understand it, some research suggests that CBD may help conditions such as:

  • Anxiety
  • Inflammation
  • Nerve-related pain

When it comes to THC, researchers are looking into whether it could be a treatment for:

  • Muscle stiffness and spasms from MS or ALS
  • Chronic pain or nerve pain
  • Epilepsy or seizures
  • Parkinson's disease tremors
  • Nausea
  • Glaucoma
  • Appetite stimulation for people with HIV/AIDS
  • Agitation in Alzheimer’s disease
  • Crohn’s disease
  • Symptoms of post-traumatic stress disorder (PTSD)

But research on marijuana is difficult in the U.S. because of strict regulations. As it's still a Schedule I drug, scientists must follow DEA rules or face fines.

CBD vs. THC for anxiety

Some studies suggest that CBD may help reduce anxiety-like behavior in animals. But we need more research to know whether this response applies to humans. A small study did find that participants who used CBD had improved sleep and anxiety, but a larger study is needed to confirm the findings.

One study compared medical marijuana, CBD, and a placebo (fake treatment) for treating anxiety in veterans with PTSD. The research found that all three groups had significant improvements in their symptoms. But the benefits for those who got THC or CBD were no better than for those who got neither.

Another study found that lower doses of THC appear to decrease anxiety in some users, but higher doses can make other users more anxious.

Smoking or consuming THC can cause:

  • Problems with concentration, judgment, and memory
  • Dizziness
  • Breathing problems
  • Fast heart rate
  • Nausea and vomiting
  • Drowsiness
  • Loss of balance

Side effects from CBD can include:

  • Nausea
  • Diarrhea
  • Upset stomach
  • Tiredness
  • Lightheadedness
  • Crankiness
  • Low blood pressure

CBD can also change the way some medicines work. Be sure to talk to your doctor if you take CBD or THC.

Laws and regulations are changing all the time on cannabis, marijuana, and CBD.

CBD that's made from hemp is legal at the federal level, and is also legal in most states, though many have restrictions.

Many states allow marijuana either for medical or recreational use. But as far as the federal government is concerned, it's still illegal in the U.S.

As of April 2023, 38 states, three U.S. territories, and the District of Columbia have legalized medical marijuana. People in these states can use THC with a prescription.

But the FDA hasn't approved CBD or THC to treat most conditions. It has only approved Epidiolex for certain seizure disorders, and two synthetic cannabis drugs, dronabinol (Marinol, Syndros), and nabilone (Cesamet), which are prescribed mainly to control nausea caused by chemotherapy.

A review is underway that could change how marijuana is classified under federal law. In August 2023, the Department of Health and Human Services sent its recommendations to the DEA, which has the final say.

What's the difference between THC and CBD?

Both CBD and THC are compounds found in the cannabis plant. THC is psychoactive, which means it changes how your brain works. It’s the ingredient in marijuana that makes you feel high. CBD isn’t psychoactive, so it doesn’t make you high.

What's the difference between hemp, CBD, and THC?

Hemp is a type of cannabis plant that contains less than 0.3% THC, the natural compound that makes you feel “high”. Cannabis plants with concentrations of THC above 0.3% are often called marijuana plants. CBD usually comes from hemp, but it can also come from marijuana plants.