The connections between substance abuse and mental illness are complex. Often, mental health issues lead to substance use and addiction as a result of self-medication.

The misuse of substances, however, could worsen the existing mental illness and cause new conditions to develop.

Here are five common mental health disorders associated with substance misuse.

1. Major depression

This is one of the most common mental health issues in the world, but most people do not receive the correct treatment or even get diagnosed.

People who suffer from depression are more likely to have a substance addiction – to drugs or alcohol or, in many cases, both.

2. Bipolar disorder

Those with bipolar disorder have a high chance of developing substance abuse as the condition causes manic and volatile behaviour, alternating with bouts of depression.

3. Anxiety disorders

Anxiety disorder is an umbrella term that could refer to social anxiety disorder, generalised anxiety disorder, phobias, panic, post-traumatic stress disorder, or obsessive-compulsive disorder.

These conditions increase a person’s chances of addiction, usually as a result of self-medication.

4. Post-traumatic stress disorder (PTSD)

PTSD symptoms include nightmares, irritability and trouble sleeping. Coping with these often leads sufferers to alcohol or drugs.

More than half of those treated for substance abuse show signs of PTSD, complicating the treatment process.

5. Borderline personality disorder

Those with personality disorder have a distorted or rigid way of viewing the world, display signs of being antisocial, and rarely seek professional help.

Studies show that those with this condition have a lifetime addiction risk of up to 72%.

It is crucial that those seeking professional help for substance abuse at rehabilitation centres are assessed for co-occurring mental disorders. This could help in the success of the recovery process.

Dennis Relojo-Howell is the founder of Psychreg. You can connect with him on Twitter @dennisr_howell.