GlaxoSmithKline won a partial victory on Wednesday in its bid to stop Spanish drug wholesalers from re-exporting its medicines at high premiums.
The result is also mixed for the European Commission's attempts to enforce a single market in pharmaceuticals.
The world's second-biggest drugmaker was trying to stop parallel trading, whereby dealers buy medicines for export at much higher prices, in this case from Spain to Britain.
It cannot be presumed that parallel trade tends to reduce prices, the European Court of First Instance said in a statement.
But in a setback for the company, the court said Glaxo had not shown that its sales conditions had no restricting effect on competition.
In 1998 Glaxo told the European Commission of new general sales conditions for its wholesalers in Spain, but Brussels said the conditions were anti-competitive and broke EU rules.
Glaxo challenged the decision in the Court of First Instance, saying there were no actual agreements on prices.
Glaxo says parallel trading erodes its research and development budget.