Antidepressant drugs are drugs that are used to treat depression and other mood disorders. They work by increasing the levels of certain neurotransmitters in the brain, such as serotonin, dopamine, and noradrenaline.

Explanation:

- Noradrenaline is a neurotransmitter that is involved in the regulation of mood, arousal, and attention. It is synthesized and released by the sympathetic nervous system in response to stress or danger.
- Once it is released, noradrenaline is degraded by enzymes called monoamine oxidases (MAOs) and catechol-O-methyltransferase (COMT).
- Antidepressant drugs, such as selective serotonin reuptake inhibitors (SSRIs) and serotonin-noradrenaline reuptake inhibitors (SNRIs), inhibit the reuptake of serotonin and noradrenaline, respectively. This leads to an increase in the levels of these neurotransmitters in the synaptic cleft, which can help to alleviate symptoms of depression and other mood disorders.
- Another class of antidepressant drugs, called monoamine oxidase inhibitors (MAOIs), inhibit the activity of monoamine oxidases, the enzymes that degrade noradrenaline and other neurotransmitters. This also leads to an increase in the levels of these neurotransmitters in the brain.
- By inhibiting the degradation of noradrenaline, antidepressant drugs can help to maintain higher levels of this neurotransmitter in the synaptic cleft, which can improve mood, increase energy levels, and improve cognitive function.

Therefore, the correct answer is option C, antidepressant drugs.