Treatments: CBT and drugs

Cognitive behavioural therapy (CBT) is based on the idea that thoughts affect feelings and behaviour.
Depression: the therapist helps the client identify negative, irrational thoughts and challenge them, replacing them with more realistic ones. Clients may keep a thought diary and do homework, such as planning enjoyable activities. It usually involves a set number of sessions.
Addiction: the client identifies triggers (people, places, feelings) and the thoughts that lead to using ('I need a drink to relax'). They learn coping skills to manage cravings and plans to prevent relapse.
Strengths: effective for many people; no physical side effects; teaches skills for the future, reducing relapse.
Weaknesses: needs motivation and effort; takes time and can be costly; may not suit people with severe depression who struggle to engage; does not address biological causes.

Antidepressants, such as SSRIs (selective serotonin reuptake inhibitors, for example fluoxetine), block the reuptake of serotonin at synapses, so more serotonin stays available. Older types include tricyclics.
Strengths: easy to take; cheaper and quicker to start than therapy; can lift mood enough for a person to engage with CBT.
Weaknesses: side effects (such as nausea or headaches); usually take a few weeks to work; treat symptoms rather than causes, so symptoms can return when the person stops taking them.

Methadone is used to treat heroin addiction. It is a legal, longer-lasting substitute that reduces cravings and withdrawal, given in controlled doses that can be reduced over time.
Nicotine replacement therapy (patches, gum) helps smokers by providing nicotine without the harm of tobacco smoke.
Strengths: reduces withdrawal symptoms; reduces harm and crime linked to illegal drug use.
Weaknesses: can replace one dependence with another; side effects; does not address psychological triggers, so relapse is possible.