There are shortages for 341 drugs, including 43 listed as critical, which could cause "life threatening or serious impact on patients", the Therapeutic Goods Administration says.

"There is not likely to be sufficient supply of potential substitutes," the TGA said of the critical drugs.

Among the critical drugs are Warfarin sodium (to treat blood clots); acetylcysteine (used to treat certain lung diseases); and calcium folinate (to treat or prevent serious blood cell disorders).

In the first four days of August, an additional 53 drugs were added to the TGA's short supply list.

Common medications for high blood pressure, diabetes, asthma, acne and depression are also in short supply.

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There are also shortages in ADHD drug Ritalin; chemotherapy drug Elotuzumab; and a critical drug used to dissolve blood clots (thrombolysis) in the immediate period following a heart attack is also in short supply.

"A medicine shortage occurs when there is unlikely to be enough of a medicine in Australia for the people who need to take it," the TGA states.

In a previous alert, the TGA said for many medicines, there is more than one brand available.

"Your pharmacist will often be able to supply a different brand if the brand you have been taking is unavailable," it said.

"In some instances there are no alternative brands of the same medicine available in Australia, or there may be insufficient supplies of alternative brands. If this is the case, your doctor or pharmacist can provide reliable and practical assistance.

"They can recommend an alternative medicine or treatment, or may be able to arrange supply of a replacement product from overseas through one of the TGA's access schemes."