Medication alert: People should not buy or take these blue capsules which contain sildenafil and can harm health.

The Department of Health has found three products claiming to treat sexual dysfunction to have undeclared western drug ingredient sildenafil that can cause serious side effects.

They are Tian Huang Gu Shen Dan and Zui Xian Dan Gong Shi with the third one being unnamed blue capsules.

The department obtained these product samples from a hawker in Yau Ma Tei during an operation yesterday. They are not registered pharmaceutical products in Hong Kong.

The side effects of sildenafil include low blood pressure, headache, vomiting, dizziness and transient vision. They can interact with nitrates found in some prescription drugs and lower blood pressure to dangerous levels.

Under the Pharmacy & Poisons Ordinance products containing sildenafil must be registered before sale and can only be sold on a doctor's prescription and under a pharmacist's supervision.

The department urges people not to buy or use them, and for traders not to sell them.