Nearly halfway into 2021, a lot has happened in the investing world. We witnessed an epic short squeeze, the continued rise of cryptocurrencies, and much else besides. The market has been volatile throughout, and fears that we are heading for a downturn -- fueled in part by inflation concerns -- are still around. 

Despite all this noise, it's essential to remember one of the golden rules of investing: Buying and holding shares of great companies for a long time generally leads to great returns. Of course, no one knows what the second half of the year holds, but no matter what happens, here are two excellent companies that are worth buying and holding through the next six months and beyond: Eli Lilly (LLY 1.01%) and Pfizer (PFE 0.69%).

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Image source: Getty Images.

1. Eli Lilly

Pharma giant Eli Lilly boasts an exciting pipeline. One of the company's most interesting projects is tirzepatide, a diabetes and obesity drug currently undergoing phase 3 clinical trials. The research firm EvaluatePharma ranks tirzepatide as the most valuable pipeline project in the pharmaceutical industry, with a net present value of $7.8 billion. 

Another promising program Eli Lilly is working on is donanemab, a potential treatment for Alzheimer's disease (AD). Donanemab works by reducing the level of amyloid plaque in the brains of AD patients, which some experts believe to be one of the main causes of the disease. That is also how Biogen's newly approved AD drug, Aduhelm, works, which explains why Eli Lilly's shares soared after Aduhelm's approval. 

Donanemab, which recently earned a Breakthrough Therapy designation from the U.S. Food and Drug Administration (FDA), proved effective in a phase 2 clinical trial, and it could go on to earn the green light from regulators, thereby adding another growth driver to Lilly's arsenal.

Then there is a potential once-weekly insulin product called Basal Insulin Fc (BIF) that Eli Lilly is currently developing. Given that patients with type 2 diabetes typically take insulin daily, BIF could be a big deal if approved. It delivered positive results in a phase 2 clinical trial. 

Lilly's current lineup of products is also worth mentioning. During its first quarter, ending March 31, the drugmaker's revenue grew by 16% year over year to $6.9 billion. One of the stars of the show for the company was its diabetes drug Trulicity, whose sales jumped by 18% year over year to $1.5 billion. The top line did get a boost in the first quarter from the sale of COVID-19 antibodies and favorable buying patterns caused by the outbreak.

That being said, Eli Lilly will still be in a great position once its coronavirus-related tailwinds subside. The company's current lineup and pipeline are well positioned to help deliver strong financial results year after year. That's why, despite the market's ups and downs, investors can count on this pharma stock to continue climbing in the long run. 

Piggy bank wearing a facemask.

Image source: Getty Images.

2. Pfizer 

Pfizer's coronavirus vaccine, BNT162b2, helped boost the company's financial performance in the first quarter thanks to the $3.5 billion in revenue it generated. The drugmaker reported total revenue of $14.6 billion, representing a 42% increase compared to the prior-year quarter. Such dazzling top-line growth isn't that common among well-established pharma giants. 

The company will continue to benefit immensely from its COVID vaccine, which was co-developed with German company BioNTech. In May, it announced that the FDA had granted Emergency Use Authorization to BNT162b2 for patients between the ages of 12 and 15, making it the first COVID vaccine to hit this milestone in the U.S. The pharma giant expects to record $26 billion in revenue from BNT162b2 this year, which is more than half of the revenue it recorded during the entire fiscal year 2020.

Outside the sale of its coronavirus vaccine, Pfizer's first-quarter revenue of $11.1 billion was up by 8% compared to a year ago. The company's lineup features the blockbuster anticoagulant Eliquis, which recorded $1.6 billion in the first quarter, 26% higher than the year-ago period.

Furthermore, Pfizer is running several dozen clinical trials and routinely adds new sources of revenue to its already rich lineup. Lastly, it offers a dividend yield of 3.9%, compared to the S&P 500's yield of 1.37%, which makes it attractive for income-seeking investors. All things considered, Pfizer also looks like an excellent stock to buy and forget.