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Anytime you read about a supposedly safe investment in anything, be nervous. That's exponentially true for biotech. However, some investment options are relatively safe compared to others. This is also true for biotech.

What makes a biotech investment relatively safe? Strong growth prospects are a must-have. Some kind of diversification is helpful, perhaps in a broad portfolio of drugs. A valuation that doesn't cause nosebleeds is also nice. Which biotech investment options fit these criteria the best? Here are three that appear to be relatively safe amid the wide array of choices in this industry.

1. Market Vectors Biotech ETF (NASDAQ:BBH)
Going with an exchange-traded fund, or ETF, is the easiest way to diversify. There are a handful of biotech ETFs, but the Market Vectors Biotech ETF deserves the nod if relatively safety is an investor's primary concern.

Source: Van Eck Global. 

This ETF holds its largest positions in biotech's version of blue-chip stocks. These top holdings include the companies with the biggest market caps that already have successful products on the market. Also, Wall Street projects double-digit growth for most of the top 10 holdings in the Market Vectors Biotech ETF, which combine for over 70% of the ETF's total assets.

Valuation could be a concern for some, though, with a price tag that is 23 times trailing 12-month earnings. However, that's a little less than some other biotech ETFs. Plus, the forward earnings multiples for the main holdings in the Vectors Biotech ETF offer another valuation perspective that isn't as scary. 

2. Gilead Sciences (NASDAQ:GILD)
Simply listing other biotech ETF alternatives would be too easy, so instead let's look at individual biotech stocks that provide some degree of relatively safety. I believe Gilead Sciences sits at the top of that list.

Source: Gilead Sciences

Gilead is by far the biggest biotech in terms of market cap. It claims seven different drugs that each generated more than $1 billion in sales last year. Only one of them, Viread, stands to lose patent exclusivity within the next five years.

Hepatitis C drugs Harvoni and Sovaldi have powered enormous earnings growth for Gilead. However, the company has also benefited from strong sales growth within its HIV franchise and cardiovascular drugs. Analysts expect this sizzling growth to taper off over the next few years. However, Gilead's $14.5 billion in cash, cash equivalents, and marketable securities give it ample ammunition to make acquisitions that could fuel additional growth.

From a valuation perspective, few biotech stocks look as appealing as Gilead. Its trailing price-to-earnings multiple of 14 is well below that of other biotechs and many large companies with less growth potential. 

3. Celgene (NASDAQ:CELG)
Celgene ranks as another big biotech that seems to be a comparatively safe investment choice. Granted, Celgene's drug portfolio isn't as diversified as Gilead's, with blood cancer drug Revlimid driving nearly 65% of sales in 2014. However, other Celgene drugs are coming on strong and should make the company less dependent on Revlimid.

Source: Celgene.

Growth doesn't appear to be a problem for Celgene in the years ahead. Revlimid's sales growth remains in the double-digits, and the drug could be approved for additional indications in the future. Abraxane, Pomalyst, and Otezla should also kick in significant revenue. Wall Street expects earnings to grow by 25% annually over the next five years.

Celgene's P/E multiple of 47 might cause some trepidation. However, remember that the market focuses much more on future prospects than on the past. When future earnings growth is factored in, Celgene's valuation looks much more palatable, with an earnings multiple of 18 based on next year's earnings.

Qualifying even more
Investing in any of these options would have made you plenty of money over the past few years. All three of these investments have more than tripled over the last half-decade. The Market Vectors Biotech ETF has performed the best, soaring 270% during the period.

It's important to note, though, that all three investments also experienced big drops during that period. The Market Vectors Biotech ETF fell nearly 20% at one point last year. So did Celgene and Gilead Sciences.

Any or all of these investments could fall by large percentages again. If you're looking for safe alternatives that have low odds of these kinds of declines, stay away from biotech. On the other hand, if you don't mind trading some risk for the potential for solid rewards, you probably won't find many other biotech investment options as relatively safe as these.