The month of August was a disappointing one for the S&P/ASX 200 (Index: ^AXJO) (ASX: XJO). The benchmark index dropped 2.3% during the month, finishing down at just 5,433 points.

But if you think that was a bad performance, spare a thought for the shareholders of these four shares:

Acrux Limited (ASX: ACR)

The shares of this pharmaceutical company dropped by a massive 49% in August following an announcement that a US court ruled that its Axiron testosterone treatment patents are not valid and therefore would not be infringed by generic competitors. As Axiron contributed 84% of Acrux’s total half year sales, this is clearly a disaster for the company. Management expects the ruling will cause a material decline in Axiron’s sales and the royalties it receives from them.

G8 Education Ltd (ASX: GEM)

The leading childcare operator’s share price dropped 20% in August after a disappointing half year result. G8 Education reported a 12% drop in statutory net profit after tax to $25 million as a result of additional borrowing costs due to early debt repayment. Unfortunately opinion is largely divided on the company and its future prospects. Some investors see it as a value trap, whereas others see it as a great source of income thanks to its forecast full year fully franked 7.9% dividend.

Monadelphous Group Limited (ASX: MND)

The share price of this multi-disciplinary engineering company fell 18% in August after its full year results revealed the full impact falling commodity prices were having on its business. In FY 2016 revenue fell 26.8% to $1.4 billion and net profit after tax fell 36.7% to $67 million. The poor performance was driven almost entirely by its Engineering Construction segment which posted a 39.2% drop in segment revenue to $757.6 million.

Northern Star Resources Ltd (ASX: NST)

The leading gold producer’s shares dropped 23% in August despite releasing full year results which revealed a 65% jump in net profit after tax to $151 million. Most of Australia’s gold producers have been on the decline recently following drops in the gold price and a subdued outlook for the precious metal. Unfortunately with many believing the US Federal Reserve could be on the verge of raising interest rates, these declines could yet extend into September.

Lastly, now might be as great a time as ever to look to see if you have either of these three wealth-destroying ASX shares in your portfolio.

3 Rotten Shares to Sell, and 1 to Buy Today

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Motley Fool contributor James Mickleboro has no position in any stocks mentioned. The Motley Fool Australia has no position in any of the stocks mentioned. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy. This article contains general investment advice only (under AFSL 400691). Authorised by Bruce Jackson.