For GlaxoSmithKline, the growing presence of generic competitors in its product suite has been a persistent drag on earnings. Meanwhile Vodafone has been smacked by rising competition and challenging economic conditions in its European heartland.
But could the tide be about to turn for both companies?
Well, GlaxoSmithKline isn't expected to put the problem of patent expirations behind it just yet. For example, sales of its critical Avodart prostate treatment slumped 42% between October and December to £110m. The decline was due to a loss of exclusivity in the US at the start of the period.
And tanking sales of the Seretide/Advair asthma treatment -- a drug that accounts for two-thirds of revenues at GlaxoSmithKline's Respiratory arm -- underlines the scale of these competitive pressures. Global sales of £3.7bn last year represented a 30% decline from their peak in 2013.
Still, I believe GlaxoSmithKline is in great shape to put these travails behind it, even if it has a long road ahead of it. The company expects to make 20 new regulatory submissions by the close of the decade and another 20 in the following five-year period. And the Brentford firm believes that "80% of the medicines and vaccines... have the potential to be 'first-in-class'."
There's no guarantee that these products will ever see the light of day of course, such is the unpredictable nature of drugs development.
But with GlaxoSmithKline doubling-down on its R&D investment in recent times, not to mention boosting its organic pipeline with shrewd acquisitions in hot growth areas, I believe the firm should make good on its development programmes.
Ring up roaring returns
Mobile operator Vodafone has also experienced persistent top-line troubles thanks to challenging conditions on the continent.
The business saw group organic service revenues slide 1.6% in the year to March 2015 as enduring weakness in Europe dragged the top line lower -- sales on the continent fell a colossal 4.7% during the period.
But the fruits of Vodafone's Project Spring organic investment programme in its data and voice coverage is helping to propel European turnover higher again. On top of this, shrewd M&A activity in the multi-services market -- like the firm's decision last month to merge its Dutch operations with those of Liberty Global -- is also transforming the top line.
These actions caused continental turnover to slip by a more modest 1.3% between last April and September, and organic service revenues fell by just 0.6% in the most recent quarter.
It appears to be a matter of time before Vodafone's sales in Europe -- a territory responsible for two-thirds of group revenues -- finally flip into the black. And with sales in Asia, the Middle East and Africa also taking off, I reckon Vodafone is on course to deliver stunning returns in the years ahead.
But Vodafone and GlaxoSmithKline aren't the only London-quoted stock stars waiting to turbocharge your investment portfolio.
Indeed, this special wealth report written by The Motley Fool's crack team of analysts identifies what I believe is one of the best growth stocks money can buy.
Our BRAND NEW A Top Growth Share report looks at a brilliant FTSE 250 stock that has already delivered stunning shareholder returns, and whose sales are expected to top the magic £1bn marker in the near future.
Click here to enjoy this exclusive 'wealth report.'It's 100% free and comes with no obligation.
Royston Wild has no position in any shares mentioned. The Motley Fool UK has recommended GlaxoSmithKline. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.