Introduction to heroin

Heroin is a powerful drug classified as an opiate, meaning it originates from the opium poppy plant. It is created by chemically modifying morphine, another substance derived from the same plant. This alteration makes heroin highly potent and addictive.

Mode of action of heroin in the brain

Heroin works by interfering with the brain's natural chemical systems, particularly those involved in pain relief and pleasure.

How heroin affects brain chemistry

Heroin enters the brain and mimics a huge surge of endorphins. It binds to opioid receptors on the dendrites (branch-like structures that receive signals) of neurones. Normally, the body produces moderate levels of endorphins during everyday activities, stress, or pain, which then trigger dopamine release for a sense of wellbeing. Heroin exaggerates this process by flooding these receptors, blocking pain signals and overwhelming many brain areas.

Once in the brain, heroin converts to morphine. This form stops the release of GABA, which usually prevents excessive dopamine from being released. As a result, dopamine levels soar, creating intense feelings of elation and pleasure reported by users.

Effects of heroin on the body and mind

Heroin primarily acts as a depressant, slowing down various bodily functions.

Short-term effects

• Respiratory changes - Breathing slows and becomes shallower, which can be dangerous and is a common cause of overdose deaths.
• Cardiovascular effects - The heart rate decreases, and peripheral blood vessels expand, making the user feel warm, flushed, and sweaty.
• Gastrointestinal impact - Digestion slows, leading to constipation and nausea as food moves more slowly through the intestines.
• Perceptual alterations - Time feels like it passes more slowly, and the drug's analgesic (pain-relieving) properties create a sense of calm, often accompanied by an intense 'rush' of euphoria. This rush peaks quickly after injection (around 5 seconds) or within minutes if snorted or smoked.

Long-term effects

• Health risks - Repeated use increases the chance of infections, collapsed veins from injections, and blockages in blood vessels due to contaminants in the drug.

Development of tolerance to heroin

Tolerance occurs when the body adapts to a substance, requiring more of it to achieve the same effects. With heroin, this happens rapidly due to changes in brain chemistry.

How tolerance develops

The brain becomes overwhelmed by the artificial flood of endorphin-like chemicals from heroin. In response, a process called downregulation takes place: neurones adjust by becoming less sensitive to these chemicals. They adapt to operate with the high levels introduced by the drug, meaning the natural levels of endorphins are no longer sufficient.

As a result, users need to take larger doses or use the drug more frequently to experience the same euphoria or pain relief. For example, tolerance can build so quickly that dosages might increase up to eight times within 4-6 months. The brain compensates by reducing its own endorphin production, making the drug's effects harder to achieve.

Eventually, even high doses fail to produce the initial high, and users continue taking heroin mainly to avoid uncomfortable withdrawal symptoms. At this stage, tolerance has led to addiction, where the drug is needed just for the body to function normally. Regular users can tolerate amounts that would be fatal to non-users.

Physiological and psychological dependency on heroin

Heroin causes both physiological (physical) and psychological (mental) dependency.

Physiological dependency

This form builds quickly as the brain adapts to heroin's presence. Without the drug, neurones that have adjusted to high chemical levels fail to fire properly with only natural neurotransmitters. This leads to withdrawal symptoms, prompting users to take more heroin to restore normal functioning. As tolerance increases, so does the need for larger doses to prevent these symptoms.

Psychological dependency

Users become driven to recreate the drug's satisfying effects and avoid the distress of withdrawal. This can dominate their thoughts, leading to behaviours like neglecting family, friends, or responsibilities. The focus shifts to obtaining the next dose, sometimes involving risky actions such as stealing. Feelings of confusion, anxiety, restlessness, or paranoia emerge when not using, intensifying the psychological pull.

Withdrawal from heroin

Withdrawal happens when a dependent user stops taking heroin, and the body struggles to readjust. Symptoms begin 8-14 hours after the last dose, peak between 30-80 hours, and usually subside within five to ten days. Their intensity depends on the level of addiction, as the body compensates for the drug's absence by overcorrecting, producing effects opposite to those of heroin.

Key withdrawal symptoms

• Initial reactions - Agitation, restlessness, and aggression, with alternating hot and cold sensations and goosebumps (sometimes called 'cold turkey').
• Respiratory and physical discomfort - Short, jerky breathing; 'itchy blood' leading to compulsive scratching; cramps, vomiting, and diarrhoea.
• Other effects - Sweating, shaking, twitching limbs, dysphoria (intense unhappiness), and nausea.