How do alkaloids cause addiction?

What do nicotine, codeine, morphine, caffeine, and diamorphine (better known as heroin) all have in common? If you said they’re all addictive substances, you’re right. Specifically, these addictive substances belong to a group of molecules called alkaloids.

What are alkaloids?

Alkaloids are naturally-occurring compounds that occur in some groups of plants. More than 3 000 different types of alkaloids have been identified in plants. Morphine and codeine are derived from a substance found in the seed capsules of the opium poppy (Papaver somniferum). 

Nicotine, also an alkaloid, is found in plants in the nightshade family like cauliflower, tomatoes, eggplants, potatoes and tobacco.

Did you know? 

You would have to eat about 350 large tomatoes to ingest as much nicotine as you would sitting next to a chain-smoker for three hours. 

Scientists aren't entirely sure why some plants produce alkaloids. It may be linked to a plant's seed development process. Scientists also think that alkaloids might protect plants against insects that eat them. It could be like a plants’ warning call saying “Hey, get away from here, leave my leaves alone!” The alkaloids the plants produce usually have an effect on an insect’s nervous system. Also, they often make the plant taste bad so that insects will learn to avoid them.

What is the chemical structure of alkaloids?

Alkaloids are a diverse group of chemical compounds. Compounds are substances formed when two or more elements are chemically bonded together. Scientists classify compounds by the groups that create them. Alkaloid compounds contain an amine group. An amine group contains a nitrogen atom and a lone pair of electrons. 

In general, an alkaloid is made up of: 

• an amine group;
• one or more carbon atoms; and
• multiple hydrogen atoms (H). 

How does the chemical structure of alkaloids vary? 

Let’s compare the structure of two alkaloids — morphine and heroin. Morphine is a strong prescription drug that many doctors prescribe as a painkiller. Heroin is a strong non-prescription drug that is illegal in Canada. Both morphine and heroin are narcotics, which are now more formally called opioids. 

Did you know? 

Heroin was first sold as a cough suppressant and a substitute for morphine. 

Morphine and heroin have a similar chemical structure. Both have a benzene ring and an amine group. However, the structures of each of the compounds have different functional groups. These are groups of atoms within a molecule that give the compound its unique characteristics. Chemists use functional groups to classify different compounds. For example, morphine and heroin differ by two functional groups. Morphine has two alcohol, or hydroxyl, functional groups (-OH). Heroin, on the other hand, contains two ester functional groups (-OCOCH₃) in place of morphine’s two hydroxyl groups. 

How do alkaloids affect humans?

We know that alkaloids affect insects, but how do they affect people? Some alkaloids, like morphine and codeine, are taken because they relieve pain, but they can also make people feel sleepy. Nicotine can make people feel calm, relaxed and even euphoric. Why the difference?

Human brains have reward pathways. Everyday actions, such as eating a piece of chocolate or drinking a glass of water when you’re very thirsty, can trigger the reward pathways in your brain. However, other things can also trigger these reward pathways, like alkaloids.

Let's look at morphine. When a patient is given morphine, it binds to opioid receptors in the body’s neurons. This reduces the pain signal that is sent to the brain. It also activates the reward system and likely increases the production of endorphins, which are like the body’s own opiate. Endorphins are produced in response to activities such as creative pursuits, exercise and social activities.

Did you know? 

The first reference to opium as a feel-good substance may be as early as 3 400 BCE! In fact, ancient Sumerians called it the “joy plant.” 

Morphine also releases a chemical called dopamine in the brain. It was once thought that dopamine was responsible for the feelings of euphoria (the “high”). But now scientists think dopamine may actually be responsible for getting us to repeat pleasurable activities. 

How do people get addicted to alkaloids?

When a person takes an addictive drug over time, that person may develop a tolerance for it. You can think about this process like a push-up exercise challenge. On the first day, you can only do one push-up. If you keep practicing every day, after 20 days, you can probably do many more push-ups. That one push-up you did on day one will seem easy. 

Let’s imagine a similar process with a person taking morphine. After a person has taken morphine many times, it’s harder for the body to produce endorphins. Also, it will be harder for the body’s reward pathways to produce dopamine without a little boost of morphine. As a result, a person may feel that they need morphine to feel “okay.” Over time, a person may need larger and larger doses of the drug, and find it very difficult to stop taking it. This is known as drug dependence. Addiction is more than just a dependence on a certain drug. It is a chronic health condition with many impacts on people, both physical and mental.

Summing up

Alkaloids have been useful to humans in our past and present. Painkillers such as codeine and morphine make life bearable for many people. And for some people, the day cannot start without a cup of coffee or cola. But as you’ve just learned, alkaloids impact the brain’s reward pathway which can make them very addictive. 

If you or someone you know is struggling with addiction, speak with a medical professional.