Which of the following is responsible for the mood changes/depression in humans?

Noradrenaline

The correct answer is option 3. Noradrenaline.

Noradrenaline, also known as norepinephrine, is a neurotransmitter that plays a role in mood regulation. Imbalances in noradrenaline levels have been implicated in mood disorders, including depression. Antidepressant medications often target the regulation of neurotransmitters, including noradrenaline, to alleviate symptoms of depression.

The other options:

(1) Thyroid:
The thyroid gland produces hormones (thyroxine and triiodothyronine) that regulate metabolism. Thyroid disorders can impact mood, but they are not the primary neurotransmitter associated with mood changes.

(2) Norethindrone:
Norethindrone is a synthetic progestin commonly used in hormonal contraceptives. While hormonal changes can influence mood in some individuals, norethindrone is not primarily responsible for mood changes associated with depression.

(4) Terfenadine:
Terfenadine is an antihistamine that was previously used to treat allergies. It is not directly related to mood changes or depression.

In summary, noradrenaline is the neurotransmitter associated with mood changes and depression in humans.